Electrical measurement of the surface of a living body, the skin, for example, is important in the field of electrophysiology, and is being practically applied to a polygraph and various types of diagnostic instruments in acupuncture and moxibustion. It is known that when measuring the electrical characteristics of the skin, the magnitude of voltage being applied and the duration of voltage application have a significant influence on measurement results. Application of too high a voltage could cause the electrolysis of water and/or dielectric breakdown in and out of adjacent cells. Such irreversible phenomena become pronounced when voltage application lasts longer. Application of a voltage of 10 volts for a few seconds can hardly obtain satisfactory reproducibility in the measurement of the d-c resistance of the skin. That is, a d-c measurement by applying a voltage of approximately 10 volts is nothing more than a kind of breakdown test. In order to perform proper measurements in a range where Ohm's law holds, it is necessary to apply a lower voltage for a duration as short as possible.
The surface and the inside, i.e., internal organs, of a human body are strongly linked to each other with the autonomic nervous system. Any disturbance of an internal organ is therefore indicated by a paresthesia at a particular location of the body surface governed by the autonomic nerve belonging to the same vertebral segment. This is a phenomenon known as the viscerosensory reflex, which is frequently used as a diagnostic means. Furthermore, the human body is a total system in which not only individual organs and tissues are combined while maintaining independence with each other, but also autonomic nervous, hormone and other systems have extremely complicated and delicate effects upon each other via unknown interactions. The surface and inside of the body are linked to each other by means of an entire system of such interactions.
Medical electronic engineering has made remarkable progress in recent years to such an extent that modern medical science relies almost entirely on instrumental diagnosis. Most of these diagnostic instruments, however, are dedicated to local diagnosis of the inside of the human body using X rays, ultrasonic waves, etc. Prices of instruments as well as their operating costs are usually extremely high. Furthermore, these instruments often cause abnormal stimuli to the human body, and some of them may leave a certain degree of impairment after diagnosis in extreme cases.
In view of this, the present inventor et al developed and proposed an internal organ-autonomic nervous function diagnostic system for diagnosing the "Keiraku" and the function of an internal organ to which the Keiraku belongs on the basis of parameter values characterizing changes over time in the current obtained by applying a rectangular-wave pulse voltage of 1/1,000 seconds and less than 3 volts to a location, called the "Seiketsu" according to acupuncture/moxibustion medicine, on fingers and toes (Japanese Patent Publication 52-4878; U.S. Pat. No. 3,971,366). In the following, the system according to this proposal will be referred to as the prior-art system.
The phenomenon on which the prior-art system relies was novel and not publicly known. That is, an electric current I (t) corresponding to a rectangular-wave voltage applied to the skin is a transient current which reaches the maximum value immediately after voltage application, and then attenuates within only several tens of microseconds into an almost constant d-c component. FIG. 1 shows the waveform of this transient current. The maximum current flowing in the initial stage is called the pre-polarization current BP, and the eventually stabilized d-c current is called the post-polarization current AP; the BP being several dozen to a hundred times as large as the AP. It is concluded on the basis of various tests conducted later that this current flows inside the corium.
In addition to the AP and the BP, a total amount of charge participating in polarization IQ and a current attenuation time TC are defined as shown in FIG. 1. That is, the total charge IQ is defined as a shaded area in the figure, and the attenuation time TC as the time expressed by a point 120 at which a tangent 100 at the BP of the current curve intersects with a straight line 110 drawn at the AP value in parallel with the time axis. These four parameters BP, AP, TC, IQ are effective in the Keiraku diagnosis in acupuncture/moxibustion medicine. In the prior-art system, the diagnoses of the Keiraku and the functions of internal organs are carried out on the basis of these parameter values at each Seiketsu and the horizontal and vertical balances among them. In the following description of this Specification, these parameters will be referred to as the transient characteristic parameters.
The prior-art system is based on the principle of the Oriental medicine, in which changes in the functions of internal organs are grasped on the basis of the flow of "Ki" in the Keiraku. Although the "Keiraku" has not necessarily been clearly explained in terms of modern medicine, its relations with autonomic nerves and the transmission mechanism of body fluids are now being earnestly studied.
The aforementioned measuring method on the basis of the transient characteristic parameters in the prior-art system is a new departure from the theory that had been widely believed in dermato-electrophysiology that the corium has no relations with the electric characteristics of the skin. A large number of dermato-electrophysiologic studies have been made public and several equivalent circuits corresponding to the characteristics of the skin have been proposed on the basis of experiments. However, the fact is that these equivalent circuits do not coincide with each other, and as a result, no clear-cut conclusion has been reached as to the correlationship between these equivalent circuits and the microscopic structure of the skin. This is because the skin of a living body is of a very non-linear and active nature and has complex frequency characteristics. That is, the behavior of the skin greatly varies depending on the amplitude, waveform, frequency range of the electrical signal applied.
In this respect, the aforementioned prior-art system succeeded in obtaining measurements in linear ranges where no researchers had realized such measurements by reducing the voltage applied and the duration of voltage application, and this led to a conclusion that overthrew the established theory. The defined four transient characteristic parameters AP, BP, TC and IQ, however, just represent apparent features of the waveforms and are not based on the accurate analysis of the waveforms. That is, in the prior-art system, the purpose of which is limited to the diagnosis of the functions of the Keiraku--internal organ in acupuncture/moxibustion medicine, parameters have been required only to represent the functions of the Keiraku--internal organ, and no accurate analysis in terms of equivalent circuits has been required. Thus, the prior-art system has been limited to an extremely narrow applications, such as the Keiraku diagnosis at the Seiketsu.
In the prior-art system, parameters have not always been determined with high accuracy from current data because current waveforms have not been analyzed. This problem is pronounced particularly with the parameters BP and TC. In the aforementioned U.S. Pat. No. 3,971,366, the parameter BP is substituted by a peak value measured in the peak-hold circuit. Due to the deformation in current waveforms caused by the pre-amplifier (which is particularly remarkable in the initial stage of current change), however, the peak value tends to be lower than the true BP value. Furthermore, there is another problem of poor accuracy because the BP value is determined with the data obtained at a single point. In another method, the parameter BP is determined by selecting several points in the initial stage of current change, and adjusting these points to a polynomial or an exponential function. Since it is impossible to contain many points in these functions with this method, only the data at two or three points are used to determine the parameter BP. It is impossible therefore to improve measuring accuracy by overcoming random noises. The parameter TC, on the other hand, can be determined by extrapolating the functions obtained as they are. This method of determining the parameter TC, in which the functions determined on the basis of the data at two or three points within a considerably shorter period than the attenuating time of the attenuating function, can result only in low reliability of the results.
In general, it is very important to obtain correct electrical equivalent circuits by analyzing current waveforms. It is only by this method that the relationship between the current waveform parameters or equivalent circuit parameters and the anatomical structure of the skin can be established. Furthermore, it is by this method that changes in the characteristics of the skin detected by electrical measurement can be explained microscopically.
It can be expected that the electrophysiological characteristics exhibited by the surface of a living body may vary with different locations on the surface of the living body. Consequently, if a correct analysis method in terms of equivalent circuits can be established corresponding to the structure of the skin, such an analysis method can be readily applied to any given locations on the surface of the human body.
Having a complicated structure, the skin naturally must have complicated frequency characteristics, an impedance analysis using a sine wave of a single frequency cannot be a correct method. In this respect, using a rectangular-wave pulse having a short rise time, as in the prior-art system, would be far more advantageous than an analysis using sine waves because such pulse signals have a very wide Fourier spectrum.
To find a correct equivalent circuit of the skin not only is electrophysiologically meaningful but also opens up a very wide range of applications. In other words, with such an equivalent circuit, the surface structure of living things, whether animals or plants, can be subjected to electrophysiological analysis. In this way, if a more universal method of electric equivalent circuit analysis that can be applied not only to human beings but also to animals and plants is established, it can be applied to a very wide range of applications, including inspection of the freshness of fruits, monitoring of the growth of agricultural crops.